Hydraulically operated mine prop



Jan. 26, 1965 E. BLENKLE v 3,165,991

' 'H YDRAULICALLY OPERATED MINE PROP 1Fi1edApri1 12, 1962 2 sheets-sheet 1 F/GJ 24 3f sa 30 4 Y G 1:. 2g 32 3 35 1 23d 0 g as: g

7 ,4 /2` /3 /f l 4 3- l 6 je V J /NvfA/oR Jan. 26, 1965 2 shets-sheet 2 Filed April 12, 1962 /NVE/vrof? fw .El el Erwin ilenirle, Bochum, Germany, assignor to Bochumer Eisenhtte Heintzmann Co., Bochum, Germany, a

firm

Filed Apr. 12, 1962, Ser. No. 1873127 Claims priority, application Germany, Apr. 2h, wel,

1s norms. ci. itz-toa) :This nventionrlates to mine props, and more Specically to a hydraulically operated mine prop.

The common hydraulically operated mine `props comprise an external and an internal prop member andare provided at the inner end of the internal prop member with a prop piston which is longitudinally shiftably guided within the external prop member serving as a pressure chamber and is sealed in a huid-,tight manner relative to the inner wall of the external `prop member. In the hydraulically operated mine props used in practice the prop piston is always rigidly connected to the `internal prop member and in itself rigidly constructed.

These known hydraulically operated mine props `have the disadvantage that, in order to ensure a reliable sealing between the external prop member and the internal prop member and to permit an easy slippingof the prop members into and out of each other, as a rule, six diiferent surfaces of the prop members, partly of considerable dimensions, rnust be worked with particular care and the prop members connected with and guided within one another must be accurately centered at three points of the mine props. First the internal prop member `must be centered relative to the inner wall of the external prop member serving as pressure chamber and this requires a careful working of the` surfaces of the prop `piston and of the inner wall of the external prop member guided on one another. Furthermore, the outer `wall oi the internal prop member must be centered relative to a guide member provided at the inner end of the `externalprop ,member and this again renders necessary an accurate working of the surfaces thereof guided on one another. Moreover, in

quired between the prop piston rigid in itself and the `inner end of the `internal prop member to which the prop -piston is rigidly secured so that two further surface sections must be carefully worked. Such a threefoldcentering inevitable in the known hydraulically operated mine props can, as a rule, only be obtained with the required accuracy when precision-made steel tubes are used. Such precision-made steel tubes are naturally considerably more expensive than common commercially obtainable tubes which have not been subjected to `a iine working.

Practice has shown that owing to the great ratio of slenderness of the common `hydraulically operated mine props and their frequently eccentric loading, a slight canting of the internal prop member relative to the external prop member cannot be avoided in spite of the prop members which are longitudinally shiftably arranged within one another b eing doubly guided by the prop piston and the guide member provided at the inner end of the external prop member. Such canting of the internal prop member relative to the external prop member owing to the rigid construction of the prop piston and its likewise rigid mounting on the internal prop member results in the prop piston being also canted relative to the inner wall of the external prop member and its sealing surfaces no longer uniformly engaging the inner wall of the external prop member in all places. Owing to the high fluid pressures of 400 to 500 atmospheres prevailing in the pressure chambers of hydraulically operated mine props, this has the disadvantageous result that the sealing between United States Patent() V.involving a considerable amount of cost and labour.

the prop piston and the inner wall of the external prop member will become untight causing an extremely undesirable reduction in the carrying capacity of the props. Such canting of the internal prop member together with the prop piston relative `to the external prop member moreover results in irregular wear of the packings provided on the piston and also involves the risk of the piston being jammed in the external prop member. Such failure often cannot be remedied in `situ but requires repair in special aboveground or underground repair shops and this necessitates a transportation of the props to `these workshops A canting between the external and internal prop member or the piston must be apprehended primarily in cases where the prop, as is often the case in underground mine workings, must not only take up axially directed forces but also loads directed more or less transversely of the axis of the prop. This is especially the case when the hydraulically loperated mine props are employed in a medium steep-angle or steepangle position and/or serve as abutmentsor for supporting conveyors and winning machines.

lt `is the object Vof the present invention to overcome the aforedescribed disadvantages of the known mine props.

This object is achieved according to the invention by providing `a hydraulically operated mine prop which comprises an Vexternal prop member closed at one end, an internal prop member projecting into said external `prop member, and a prop piston secured to the inner end of .said internal prop member and longitudinally slidably and tion of said `prop piston serving as a connecting `portion and the connecting portion of said prop piston having over at least part of its axial length such an elastic deformability as to permit limited canting of the sealing portion to all sides relative to said internal prop member.

This arrangement permits the internal prop member to be canted in all Vdirections relative to the external prop member to a limited extent according to the actually occurring loads without producing any unfavourable effect on the guiding or sealing function of the sealing portion of theprop piston sealingly guided within the external prop member. This affords the advantage that in the case of forces acting eccentrically or directed more or less -transversely of the axis of the prop, the internalprop member can withdraw to a limited extent from its position coaxial With the longitudinal axis of the external prop member by canting to a corresponding amount whereby the sealing between the prop piston and the inner wall of the external prop member is however in no way impaired since such a canting can have no effect on the portion of the prop piston sealingly guided within the external prop member but is interceptedby the other portion of the prop piston, e.g. the connecting portion which is at least partly elastically deformable. Consequently, the sealing portion of the prop piston uniforml sealingly bears over its entire circumference against the inner surface of the external prop member even when the prop members are canted relative to one another so that the pressure chamber can neither become untight nor the prop piston be unevenly loaded or excessively worn locally or jammed.

Certain inaccuracies in the geometrical shape of the prop members and a certain roughness ofI the inner surface of the external prop member can be put up with without impairing the sealing between the sealing portion of the prop piston guided within the external prop member e@ and the external prop member itself. Even in cases where the external prop member has undergone a certain permanent deformation owing to the high mechanical strains as are unavoidable in rough mine workings, the construction of the prop proposed by the invention nevertheless ensures an almost uniformly effective sealing over the entire circumference of the piston relative to the inner wall of the external prop member.

A further advantage of the hydraulically operated mine prop proposed by the invention consists in that the guide member provided at the inner end of the external prop member can be constructed with relatively large play since the sealing portion of the prop piston guided within the external prop member owing to the elastic deformability of the connecting portion is not subjected to practically any strains and is not impaired in its sealing function when the prop members are canted relative to one another. Such a guide member having a relatively rough tolerance and located at the inner end of the external prop member can naturally be produced at relatively low cost and moreover be kept substantially more simple than is the case in the known construction. Especially this guide member and the outer wall of the internal prop member need not be accurately worked and even relatively large permanent deformations of the wall of the internal prop member cannot affect the longitudinal shiftability of the prop members.

A particular advantage of the mine prop according to the invention consists however in that contrary to the known constructions only a single centering is required between the inner wall of the external prop member and the sealing portion of the prop piston and this results in a much simpler and less expensive manufacture in comparison with the mine props hitherto used in practice. Since certain inaccuracies of the inner wall of the external prop member can be compensated by the elastic deform- Iability of the connecting portion of the prop piston, requirements as to surface quality and geometrical tolerance of the external prop member can be considerably lower than in the known props with a rigid prop piston and a rigid connection between the prop piston and the internal prop member. Y

For the manufacture of the mine prop proposed by the invention the hitherto used precision steel tubes having high surface qualities and close form tolerances can therefore be dispensed with. The internal and external prop members can rather be manufactured of common commercially obtainable tubes, only the tubes used for mak- A.

ing the external prop members requiring a simple noncutting surface treatment on their inner walls to ensure over their entire lengths a substantially uniform internal cross-section and a fairly smooth surface. Such a smoothing of the inner wall of the external prop member may, for example, be carried out by means of a mandrel and, if required, by subsequent rolling by means of a plurality of rollers rolling on the inner wall of the external prop member. Further surface treatment, especially cutting treatment, and observation of close tolerances in size and form is however not necessary even with the tubes used for making the external prop members.

Owing to the relatively rough tolerances in form, size and surfaces it is easily possible in the prop according to the invention to permit a lateral deviation of some millimetres over one metre length of tube, which is within the permissible range of tolerance in common commercially obtainable tubes, whereas in the hydraulically operated mine props pertaining to the state of the art very high requirements are made in respect of straightness of the tubes and the tubes used for making these props had, as a rule, to be reworked to eliminate whenever possible uneven places and inadmissible tolerances in form and size. For this reason it was necessary in the construction of the hitherto common mine props to obtain tubes with a wall thickness considerably greater than the final wall thickness to be able to compensate the losses in wall thickness occurring during reworking and to ensure with certainty a wall thickness meeting actual strain conditions. Contrary thereto, in the prop proposed by the invention, common commercially obtainable tubes with a wall thickness corresponding to the actually required final wall thickness can readily be used since no cutting working whatsoever is required.

ln an expedient embodiment of the invention at least the part of the connecting portion of the prop piston permitting canting of the sealing portion relative to the internal prop member consists of elastically deformable material. In this manner both sufficient canting of the sealing portion of the piston relative to the internal prop member and a connection sufficiently resistant to tension and compression of the sealing portion with the internal prop member is ensured. v

The connecting portion of the prop piston may cornprise a plurality of -sections of different elastic deformability and stability of shape arranged one behind the other in the axial direction of the mine prop. In this manner it is possible to transfer the elastic deformation occurring when the prop members are canted relative to one another into a certain section of the connecting portion of the prop piston, whereas the other sections of this portion of the prop piston are subjected to no or to a comparatively slight elastic deformation. As a rule, such a construction is to be recommended wherein the connecting portion of the prop piston is integrally constructed but has a plurality of sections of different crossysections arranged one behind the other in the axial direction of the mine prop.

According to a further feature of the invention substantially only the section of the connecting portion located adjacent the sealing portion of the prop piston may have an elastic deformability permitting canting of the sealing portion to all sides relative to the internal prop member.

The remaining part of the connecting portion, especially the part serving for connection with the inner end of the internal prop member, on the other hand, has such a stability of shape that its connection resistant to tension and compression with the internal prop member is not impaired when the prop members are canted relative to one another.

The connecting portion of the prop piston is expediently guided within the external prop member so as to leave radial play circumferentially therebetween so that the guiding and sealing function of the prop piston is exclusively performed by the sealing portion thereof, whereas the connecting portion of the piston is capable of adapting itself over its entire length to a possible canting of the internal prop member relative to the external prop member.

In a particularly expedient embodiment the sealing portion and the connecting portion of the prop piston are integrally constructed and consist of a rubber-like material, preferably an elastically deformable synthetic plastic material. The construction of the prop piston of a rubber-like synthetic plastic material of small swelling capacity, high resistance to abrasion and high imperviousness to acids and alkalies has proved especially advantageous. Such a prop piston consisting of synthetic'plastic material may be produced in a particularly simple manner, for example by casting, pressing or injection moulding or by sawing, cutting or the like out of a relatively large block of synthetic plastic material. The cost of production of such a prop piston of synthetic plastic material amounts to only a fraction of the cost of the hitherto exclusively used metal prop pistons which always require a complicated and expensive metal-cutting treatment. Moreover, such a prop piston consisting of synthetic plastic material is many times lighter than the hitherto used steel pistons with the result that the total weight of the mine prop is considerably reduced. This is of essential importance above all for such props which are intended to be used in steep-angle or medium steepangle positions where the use of hydraulically operated mine props was hitherto kept within relatively narrow limits owing to the heavy weight of the props.

Synthetic plastic materials such as polyurethane resins, for instance, the material sold under the registered trademark Vullrollan have proved especially suitable for the production of such prop pistons and are distinguished, in addition to the aforedescribed properties, by a rubber-like elasticity, suiiicient hardness, resistance to compression and abrasion as well as a high rebound elasticity.

Due to the elastic deformability of such synthetic plastic materials it is, of course, possible in the prop according to the invention to construct the sealing portion of the prop piston with slight overmeasure and to provide it, if required, on its circumference with sealing lips or ealing extensions which, when introduced into the external prop member, are sealingly pressed against the `inner wall of the external prop member and elastically deformed thereby so that thereby alone a suicient sealing is obtained between the prop piston and the external prop member and further sealings can either be completely dispensed with or given a particularly simple construction.

A further advantage of a prop piston consisting of such an elastically deformable or synthetic plastic` material consists in that the prop piston is compressed in axial direction by the huid pressure prevailing in the pressure chamber and thereby simultaneously deformed to a certain extent in radial direction and pressed against the inner wall of the external prop member so that the sealing between the prop piston and the inner wall of the external prop member is the more improved the more the pressure in the pressure chamber of the prop increases.

To ensure a suicient elastic deformability of the connecting portion of the prop piston, at least one circumferential recess of wedge-like cross-section and great radial depth may be provided in the longitudinal region of the connecting portion of the prop piston adjacent the sealing portion. The radial depth of the circumferential recess of preferably wedge-like cross-section may amount from one quarter up to a half, preferably to one third of the radius of the prop piston. Such a recess not only increases the deformability of the piston in this region, but also ensures the deformation possible in this region not to be impaired by the adjacent piston portions of greater stiffness of shape.

T he connecting portion of the prop piston expediently engages with a stud-like extension in the end face of the internal prop member and is `preferably detachably connected therewith. To obtain a connection which can be strained to a suiicient extent, it is advisable to firmly connect the stud-like extension of the connecting portion consisting of synthetic plastic material, preferably by glueing, with a metal sleeve surrounding the extension andcapable of being detachably secured to the inner end of the internal prop member by means of a screwed connection. The metal sleeve may be provided with an external thread and the inner end of the internal prop member may be provided with an internal thread int-o which the threaded metal sleeve can be screwed. A prop piston of such construction can be manufactured in a simple manner and at relatively low cost, utilizing in the aforedescribed construction the good sealing and deforming qualities and the light weight of the synthetic plastic material and nevertheless obtaining a reliable and easily detachable mounting of the prop piston on the internal prop member, the mounting being capable of withstanding all occurring strains. Consequently, the prop piston according to the invention can be, if required, dismantled and mounted in a short time and possibly replaced, if this should be necessary due to natural wear.

ln some cases it is, however, possible to dispense with such a metal sleeve provided between the piston of synthetic plastic material and the internal prop member and to connect the connecting portion of the piston directly with the inner end of the internal prop member either undetachably by giueing or detachably by means of a screwed connection. in the latter case it is,`however, to be recommended to round oif the thread provided on the prop piston of synthetic plastic material or at least to provide it with a chamfer to avoid tearing of the synthetic plastic material.

According to a further feature of the invention the prop piston may have a bore extending preferably centrally through the entire length thereof so that apart from the interior space of the external prop member `also the entire interior space of the internal prop member is sub- 4jected to the full iluid pressure and thus serves as a pressure chamber. This affords the advantage that the Viiuid pressure prevailing in the pressure chamber directly acts upon the inner sides of the head and base plates of the prop bearing against the mine roof and floor, respectively, and the compressive forces transmitted to the ends of the prop when the roof and floor `converge are directly taken up by the iiuid pressureiilling of the prop so that apart from the external prop member also the internal prop member is largely relieved of longitudinal forces and is substantially only loaded by bursting pressure.- Moreover, such a bore extending through the prop piston largely compensates the compressive forces loading the prop piston on both sides so that also particularly high fluid pressures can readily be taken up by the prop piston con- Y sisting of synthetic plastic or a similar material.

To improve the sealing function of the sealing portion of the prop pistou preferably made with slight over-measure, the sealing portion is expediently provided with a sealing lip integrally constructed therewith, facing the pressure chamber in the external prop member and adapted to be pressed against the inner wall of the externalprop member. The sealing lip may be formed, for example, by a recess in the sealing portion of the prop piston, which is in the form of an annular groove and of substantially triangular cross-section-and opens towards the pressure chamber in the external prop member. A further improvement is obtained by mounting an O-ring consisting of elastic material in the annular recess in the sealing portion of the prop piston, the O-ring being clamped against the sealing lip by a threaded ring which is screwed on the sealing portion of the prop piston and may consist of metal or also of synthetic plastic material. The threaded ring which preferably likewise consists of synthetic plastic material may, however, also be provided with an annular collar-like extension on its end face facingrthe sealing lip, the extension serving to press the sealing lip directly, i.e. without the interposition of an O-ring, against the inner wall of the external prop member.

Subject matter of the invention is further the ideato construct the head member of the prop likewise at least partly of a synthetic plastic material of high compressive strength, high cutting resistance and high resistance to abrasion, if desired, of the same synthetic plastic material as the prop piston. Such a head member is not only substantially more simple and inexpensive in its production than the hitherto used head members consisting of steel but in addition to the prop piston consisting of synthetic plastic material also provides a further substantial reduction in weight which is of particular importance when the prop according to the invention is used in steep-angle or medium steep-angle positions. Even if the head member has a relatively complicated co-nguratiomit may readily be produced just like the prop piston by casting, pressing,

injection moulding or the like in one working operation l in its iinal form so that the complicated metal-cutting treatments necessary in the hitherto used head members are dispensed with. As a rule, it is to be recommended to arrange the head member consisting of synthetic plastic material in such a manner that it forms one end wall of the pressure chamber in the external prop member and is connected to the external prop member forming the side `wall of the pressure chamber preferably by glueing so as to be resistant to tension, compression and torsion and Huid-tight. This affords the advantage that the connection between the head member of synthetic plastic matelrial and the metal tube of the external prop member is largely free from pressure strains since since the compressive forces transmitted from the roof on to the head member of the prop are directly taken up by the pressure fluid filling of the prop.

The head member of synthetic plastic material is expediently provided with a recess or bore extending transversely of the axis of the prop and serving to accommodate valves associated with the pressure chamber of the prop. Such a recess can readily be produced in one working operation simultaneously with casting, pressing or the like of the head member, i.e. without any material-cutting treatment. This recess in the head member extending transversely of the axis of the prop is expediently so constructed that it comprises a plurality of longitudinal sections of different cross-sections arranged one behind the other and the valve housings of the valves associated with the pressure chamber of the prop are constructed with corresponding cross-sections and detachably secured in the longitudinal sections of the recess. This may, for example, be achieved by providing the recess in the head member in its central longitudinal region with a cylindrical section of a relatively small cross-section in which a threaded sleeve of corresponding cross-section is mounted-if required, secured by glueing-and the valve housings having larger cross-sections are screwed into the threaded sleeve from both sides.

Two preferred embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, in which:

FIG. 1 is a longitudinal section through a hydraulically operated mineY prop according to the invention;

FIG. 2 is a View similar to FIG. l, showing part of the prop piston on an enlarged scale;

FIG. 3 is a view similar to FIG. 2, but showing part of a modification of the prop piston;

FIG. 4 is a view similar to FG. 1 and showing a modified prop piston and parts adjacent thereto, and

FIG. 5 is a view similar to FIG. 4 and showing a further modification of the prop piston.

FIG. Vl shows a hydraulically operated mine prop cornprising an external prop member 1 and an internal prop member 2 which are common commercially obtainable tubes, only the external prop member 1 having been subjected to a smoothing treatment on its inner side. A prop piston 3 is detachably secured to the inner end or the internal prop member 2 and longitudinally slidably guided in the interior of the external prop memher 1. The prop piston 3 susbtantially comprises two portions, namely a sealing portion 4 sealingly guided on the inner wall of the external prop member 1 and a connecting portion 5 connecting this sealing portion 4 with the inner end of the internal prop member 2. In the embodiment shown in the drawings the sealing portion 4 and the connecting portion 5 of the prop piston 3 are integrally constructed and consist of an elastic synthetic plastic material of small swelling capacity, high resistance to abrasion, high imperviousness to acids and alkalies and high rebound elasticity, e.g. of polyurethane resin. At the point where the sealing portion and the connecting portion d meet, a circumferential recess 6 of substantially wedge-hire cross-section is provided in the prop piston 3 and has a radial depth corresponding substantially to one third of the radius of the prop piston 3. Whereas the sealing portion 4 has a relatively great stability of shape, the connecting portion 5 is elasticaliy deformable especially in the region of the circumferential recess d to such a degree that it permits canting of the internal prop member 2 to all sides relative to the external prop member 1 or relative to the sealing portion 4 longitu- .dinally shiftably and sealing guided within the latter. The

prop piston 3 of synthetic plastic material has a central bore 7 extending therethrough for connecting in a uid conducting manner pressure chambers 8 and 9 in the internal prop member 2 and external prop member 1, respectively.

As shown in FIGS. 1 and 2, the prop piston 3 also has in the region of its sealing portion 4 a sealing lip 10 which is formed by a recess 11 in the sealing portion 4 of the prop piston 3, which is in the form of an annular groove and opens towards the pressure chamber 9 in the external Vprop member 1. In the embodiment shown in FIGS. 1

.and 2 an O-ring 12 consisting of elastic material is mounted in the recess 11 and clamped `against the sealing lip 10 by means of a threaded ring 13 which is screwed on the upper end of the sealing portion 4 of the prop piston 3. The threaded ring 13 may either consist of metal or likewise of synthetic plastic material. In the latter case it is however advisable to use synthetic plastic materials for the threaded ring 13 which have a greater compressive strength and a smaller elastic deformability than the prop piston 3. A thread 14 provided between the prop piston 3 and the threaded ring 13 is in any case expediently constructed as a square or trapezoidal thread, as shown in FIG. 2. If desired, the O-ring 12 may, however, be entirely dispensed with and the threaded ring 13 provided with an annular collar-like extension 1S of wedge-like cross-section instead thereof, as shown in FIG. 3. This extension 15 presses the sealing lip 1t) against the inner wall of the external prop member 1 when the threaded ring 13 is screwed on.

In the embodiment shown in FIG. 1 the connecting portion 5 of the prop piston 3 engages with a stud-like extension 16 formed thereon in the end face of the internal prop member 2. The stud-like extension 16 is firmly connected with a threaded metal sleeve 17 by means of an adhesive. The threaded metal sleeve 17 has an external thread 18 with which it is screwed into an internal thread provided on the inner side of the internal prop member 2 with the interposition of a sealing ring 19 constructed as an O-Iing.

The connecting portion 5 of the prop piston 3 is guided on the inner wall of the external prop member 1 with a relatively short longitudinal section 5a while leaving however a slight radial play. This is intended to avoid an excessively large lateral displacement of the inner end of the internal prop member 2 relative to the surrounding portion of the external prop member 1. A substantially larger radial play may, however, easily be provided at this point between the connecting portion 5 of the prop piston 3 and the inner Wall of the external prop member 1.

Instead of the circumferential recess 6 of wedge-like cross-section, the connecting portion 5 of the prop piston 3 may, if required, also be provided with several recesses arranged in axial direction preferably at a slight distance one behind the other and these recesses may, of course, also be given a cross-sectional shape different from that shown in the embodiment of FIG. 1.'

As shown in FIG. 1, a guide member 20 is screwed on the inner end of the external prop member 1 and has a substantially greater tolerance than the guides hitherto usual in hydraulically operated mine props and encloses the internal prop member 2 while leaving a slight radial play. An elastic centering element 21 is arranged within the guide member 2d and also serves as a dirt remover and a sealing. The internal prop member Z is provided at its outer end with a welded-on base Z2.

The external prop member 1 is provided at its outer end with a head member 23 which consists of a synthetic plastic material of high resistance to abrasion, high compressive strength and high cutting resistance, e.g. of polyurethane resin like the prop piston 3@ The head member 23 seaiingly engages with an annular extension 23a in the pressure chamber of the external prop member t plastic material.

1 and is connected thereto by means of a suitable adhesive so as to be fluid-tight and suiiiciently resistant to tension, compression and torsion. Within the head meinber 23 a recess 24 is provided which extends transversely of the axis of the mine prop and comprises a plurality of longitudinal sections of different cross-sections accommodating valves associated with the pressure chamber 9, i.e. an inlet valve 2S, a relief pressure valve 2n and a discharge valve 27. The recess 24 in the head member 23 has a central longitudinal portion 24a which communicates with a fluid channel 28 of small axial length ar-` ranged parallel to the axis of `the mine prop and opening into the pressure chamber 9 of the external prop member 1. The recess 24 in the head member 23 comprises in its central longitudinal region a cylindrical section of a relatively small diameter followed on either side by likewise cylindrical sections of larger diameter. A threaded sleeve 3l is mounted inthe central cylindrical section of relatively small diameter and ma. if desired, be firmly connected to the head member 23 by means of an adhesive. The inlet valve 25 is received in a valve housing 29l and the relief pressure valve 26 and the discharge valve 27 are lreceived in a valve housing 32 and in the head member 23, sealing rings 34 and 35 constructed as O-rings are provided. In its central longitudinal region the threaded sleeve 31 `is further provided with a connecting bore 36 corresponding to the fluid channel 28.

Contrary to the embodiment shown in the drawings, the prop piston 3 may also only partly consist of a suitable elastic material, especially a rubber-like synthetic Especially it is possible as shown in FIG. 4- to make only the connecting portion 5 of the prop piston 3 completely or partly of such an elastically 'l deformable material or synthetic plastic materiahwhereas the sealing portion 4 is formed of a material having only a slight elastic deformability. in such cases the prop piston 3 is naturally not integrallyconstructed but comprises at least two separate piston sections which are connected together, for example, by vulcanizing or glueing. It would `also be feasible as shown in FlG. 5 to construct the sealing portion 4 of the prop piston 3 of a synthetic plastic material of less elastic deformability and greater compressive strength than the connecting portion 5 and then to undetachably connect both portions together by vulcanizing or glueing or to detachably connect them together, if desired. Furthermore, it would be possible to construct also the base Z2 in the same manner as the head member 23 of synthetic plastic material, if desired. This applies especially when the base 22 is given a configuration diiferent from that shown in the embodiment of FIG. l. Finally, the mine prop shown in FIG, 1 may also be mounted, if required, in a position turned through 180 so that the head member 23 accommodating the Valves will bear against the floor and thus Will serve as the base of the mine prop.

I claim:

l. A hydraulic mine prop comprising, in combination, an external tubular prop member closed at one end; an internal prop member projecting with clearance into `said exlternal prop member and having an inner end movable toward and away from said closed end; a prop piston secured to said inner end of said internal prop member, said prop piston including a sealing portion slidably guided in said external prop member and sealingly engaging the inner surface thereof to form therewith between said closed end and said sealing portion a pressure chamber, and a connecting portion connecting said sealing portion to said inner end of said internal prop lil member for movement therewith and in a manner resistant to tension and compression, said connecting portion adjacent said sealing portion formed from elastically deformable material and having an elastic deformability in direction transverse to the axis of said piston greater than that of said sealing portion and that of the remainder of said connecting portion so as to permit limited universal tilting movement of said sealing portion of said piston relative to said internal prop member as well as limited movement of said sealing portion in direction transverse to the axis of said internal prop members, whereby slight misalignment of the prop member will result in elastic deformation of the connecting portion of said piston without aifectinguniform sealing engagement of said sealing portion with the inner surface of the external` prop member; and mcansfor feeding pressure fluid into and out of said pressure chamber.

2. A hydraulic mine prop comprising, in combination, an external tubular prop member closed at one end; an internal prop` member projecting with clearance into said external prop member and having an inner end movable to-ward and away from said closed end; a prop piston secured to said inner end of said internal prop mem-` ber, said prop piston including a sealing portion slidably guided in said external prop member and sealingly engaging the inner surface thereof to form therewith between said closed end and said sealing portion a pressure chamber, and a connecting portion connecting said sealing portion to said inner end of said internal prop member for movement `therewith and in a manner resistant to tension and compression, said connecting portion being at least in a part thereof adjacent said sealing portion formed from elastically deformable material and said part having a cross Section in direction transverse to the axis of said piston. which is smaller than the cross section of said sealing portion so as to permit limited universal tilting movement of said sealing portion of said piston relative to said internal prop member as Vwell as limited movement of said sealing portion in direction transverse tto the axis of said internal prop member, whereby slight misalignrnent of the prop members Will result in elastic deformation of said part of the connecting portion of said piston without affecting uniform sealing engagement of said sealing portion with fthe inner surface of the external prop member; and means for feeding pressure iluid into and out of said pressure chamber.

3. A hydraulic mine prop comprising, in combination, an external tubular prop member closed at one end; an internal prop member projecting with clearance into sa1d external prop member and having an inner end movable toward and away from said closed end; a prop piston secured to said inner end of said internal prop member, said prop piston including a sealing portion slidably lguided in said external prop member and sealingly engaging the inner surface thereof to form therewith between sa1d closed end and said sealing portion a pressure chamber, and a connecting portion connecting said sealing portion tto said inner end of said internal prop member for movement therewith and in a manner resistant to tension and compression, said connecting por-tion being at least in a part thereof adjacent said sealing portion formed from elastically deformable material and said part being formed with a circumferential recess having a radial depth of about one quarter to one half of the radius of said sealing portion so as to permit limited universal tilting movement of said sealing portion of said piston relative to said internal prop member as Well as limited movement of said sealing portionin direction transverse to the axis of said internal prop member, whereby slight misalignment of the prop members will result in elastic deformation of said part of the connecting portion of said piston without affecting uniform sealing engagement of said sealing portion with the inner surface il of the external prop member; and means for feeding pressure fluid into and out of said pressure chamber.

4. Ahydraulic mine prop as set forth in claim 3 in which said circumferential recess is of substantially wedgeshaped configuration and in which the depth of said recess is about one third of the radius of said sealing portion.

5. A hydraulic mine prop comprising, in combination, an external tubular prop member closed at one end; an internal prop member projecting with clearance into said external prop member and having an inner end movable toward and away from said closed end; a prop piston secured to said inner end of said internal prop member, said prop piston including `a sealing portion slidably guided in said external prop member and sealingly engaging the inner surface thereof to form therewith between said closed end and said seating portion a pressure chamber, and a connecting portion connecting said sealing portion to said inner end of said internal prop member for movement therewith and in a manner resistant to tension `and compression, said connecting portion being at least in part formed from elastically deformable material vand said part having such an elastic deformability so as to permit limited universal tilting movement of said sealing portion of said piston relative to said internal prop member as well as limited movement of said seaiing portion in direction transverse to the axis of said internal prop member, whereby slight misalignment of the prop members will result in elastic deformation of said part of the connecting portion of said piston without affecting uniform sealing engagement of said sealing portion with the inner surface of the external prop member, said prop piston being formed with a central bore extending colaxially with said piston through the whole length thereof; and means for `feeding pressure fluid into and out of said pressure chamber.

6. A hydraulic mine prop comprising, in combination, an external tubular prop member closed at one end; an internal prop member projecting with clearance into said external prop member and having an inner end movable toward and away from said closed end; a prop piston secured to said inner end of said internal prop member, said prop piston including a sealing portion slidably guided in said external prop member and sealingly engaging the inner surface thereof to form therewith between said closed end and said sealing portion a pressure chamber, said sealing portion being formed at the peripheral surface thereof with a recess in form of an annular groove opening towards said pressure chamber and forming a sealing lip adapted to be pressed against said inner surface of said external prop member, and said piston including further a connecting portion connecting said sealing portion to said inner end of said internal prop member for movement therewith and in a manner resistant to tension and compression, said connection portion being at least in part formed from elastically deformable material and said part having such an elastic deformability so as to permit limited universal tilting movement of said sealing portion of said piston relative to said internal prop member as well as limited movement of said sealing portion in direction transverse to the axis of said internal prop member, whereby slight misalignment of the prop members will result in elastic deformation of said part of the connecting portion of said piston without affecting uniform sealing engagement of said sealing portion with the inner surface of the external prop member; and means for feeding pressure fluid into and out of said pressure chamber.

7. A hydraulic mine prop as set forth in claim 6 wherein said recess is of substantially triangular cross section.

8. A mine prop as claimed in claim 7, and including an O-ring consisting of elastic material mounted in the recess in the sealing portion of the prop piston, and a threaded ring screwed on the sealing portion of the prop piston to clamp said O--ring against the sealing iip.

. tically deformable synthetic plastic material of small swelling capacity, high resistance to abrasion and high imperviousness to acids and alkalies.

1l. A hydraulic mine prop comprising, in combination, an external tubular prop member closed at one end; an internal prop member projecting with clearance into said external prop member and having an inner end movable toward and awayk from said closed end; a prop piston secured to said inner end of said internal prop member, said prop piston including a sealing portion slidably guided in said external prop member and sealingly engaging the inner surface thereof to Aform therewith between said closed end yand said sealing portion a pressure chamber, and a connecting portion connecting said sealing portion to said inner end of said internal prop member for movement therewith and in a manner resistant to tension and compression, said connecting portion being at least in part formed `from elastioally deformable material and comprising a plurality of sections of different elastic deformability and stability of shape arranged one behind the other in the axial direction of the mine prop so as to permit universal tilting movement of said sealing portion of said piston relative to said internal prop member as well as limited movement of said sealing portion in direction transverse to the axis of said internal prop member, whereby slight misalignment of the prop members will result in elastic deforma-tion of said part of the connecting portion of said piston without affecting uniform sealing engagement of said sealing portion with the inner surface of the external prop member; and means for feeding pressure uid into and out of said pressure chamber.

l2. A hydraulic mine prop -as set lforth in claim 1l wherein substantially only the section of the connecting portion located adjacent the sealing portion of the prop piston has an elastic deformability permitting univers-al tilting movement of said sealing portion of said piston relative to said internal prop member as well as limited movement of said sealing portion in direction transverse to the axis of said internal prop member.

13. A hydraulic mine prop comprising, in combination, an external tubular prop member closed at one end; an internal prop member projecting with clearance into said external prop member and having an inner end movable toward and away from said closed end; a prop piston secured to said inner end of said internal prop member, said prop piston including a sealing portion slidably guided in said extennal prop member and sealingly engaging the inner surface thereof to form therewith between said closed end and said sealing portion a pressure chamber, and a connecting portion connecting said sealing portion to said inner end of said linternal prop member `for movement therewith and in a manner resistant to tension and compression, said connecting portion being at least in part formed from elastically deformable material and said part having such an elastic deformability so as to permit imiversal tilting movement of said sealing portion of said piston relative to said internal prop member as well as limited movement of said sealing portion in direction transverse to the axis of said internal prop member, whereby slight misalignment of the prop members will result in elastic deformation of said part ofthe connecting portion of said piston without affecting uniform sealing engagement of said sealing portion with the inner surface of the external prop member, said connecting portion of said prop piston being guided within said external prop i3 member so as to leave radial play circumferentially therebetween; and means for `feeding pressure iluid into and out of said pressure chamber.

14. A hydraulic mine prop comprising, in combination, an external tubular prop member closed at one end; an internal prop member projecting with clearance into said external prop member and having an inner end movable toward and away from said closed end; a prop piston secured to said inner end of said internal prop member, said prop piston including a sealing portion slidably guided in said external prop member and sealingly engaging the inner surface thereof to form therewith between said closed end and said sealing portion a pressure chamber, and a connecting portion connecting said sealing portion to said inner end of said internal prop member for movement therewith and in a manner resistant to tension and compression, said connecting portion being at least in part formed from elastically deformable material and said part having such an elastic deformability so as to permit universal tilting movement of said sealing portion of said piston relative to said internal prop member as well as limited movement of said sealing portion `in direction transverse to the axis of said internal prop member, whereby slight misalignment of the prop members will result in elastic deformation of said part of the connecting portion of said piston without affecting uniform sealing engagement of said sealing portion with the inner surface of the external prop member, said connecting portion being formed with a stud-like extension projecting into said inner end of said internal prop member and being detachably connected thereto; `and means for feeding pressure uid into and out of said pressure chamber.

15. A mine prop as claimed in claim 14, wherein a metal sleeve surrounds the stud-like extension of the connecting portion of the prop piston and is firmly connected therewith and an external thread is provided on said metal sleeve for detachably securing said metal sleeve to the inner end of the internal prop member.

16. A mine prop as claimed in claim l5, wherein an internal thread is provided on the inner end of the internal prop member and the metal sleeve is screwed with its external thread into said internal thread on the inner end of the intennal prop member.

References 'Cited by the Examiner UNITED STATES PATENTS 2,584,926 2/52 Roll 309-17 2,912,211 11/59; Heusner 248-354 FOREIGN PATENTS 857,679 12/52 Germany.

92,916 2/ 22 Switzerland.

FRED E. ENGELTHALER, Primary Examiner. 

5. A HYDRAULIC MINE PROP COMPRISING, IN COMBINATION, AN EXTERNAL TUBULAR PROP MEMBER CLOSED AT ONE END; AN INTERNAL PROP MEMBER PROJECTING WITH CLEARANCE INTO SAID EXTERNAL PROP MEMBER AND HAVING AN INNER END MOVABLE TOWARD AND AWAY FROM SAID CLOSED END; A PROP PISTON SECURED TO SAID INNER END OF SAID INTERNAL PROP MEMBER, SAID PROP PISTON INCLUDING A SEALING PORTION SLIDABLY GUIDED IN SAID EXTERNAL PROP MEMBER AND SEALINGLY ENGAGING THE INNER SURFACE THEREOF TO FORM THEREWITH BETWEEN SAID CLOSED END AND SAID SEALING PORTION A PRESSURE CHAMBER, AND A CONNECTING PORTION CONNECTING SAID SEALING PORTION TO SAID INNER END OF SAID INTERNAL PROP MEMBER FOR MOVEMENT THEREWITH AND IN A MANNER RESISTANT TO TENSION AND COMPRESSION, SAID CONNECTING PORTION BEING AT LEAST IN PART FORMED FROM ELASTICALLY DEFORMABLE MATERIAL AND SAID PART HAVING SUCH AN ELASTIC DEFORMABILITY SO AS TO PERMIT LIMITED UNIVERSAL TILTING MOVEMENT OF SAID SEALING PORTION OF SAID PISTON RELATIVE TO SAID INTERNAL PROP MEMBER AS WELL AS LIMITED MOVEMENT OF SAID SEALING PORTION IN DIRECTION TRANSVERSE TO THE AXIS OF SAID INTERNAL PROP MEMBER, WHEREBY SLIGHT MISALIGNMENT OF THE PROP MEMBER WILL RESULT IN ELASTIC DEFORMATION OF SAID PART OF THE CONNECTING PORTION OF SAID PISTON WITHOUT AFFECTING UNIFORM SEALING ENGAGEMENT OF SAID SEALING PORTION WITH THE INNER SURFACE OF THE EXTERNAL PROP MEMBER, SAID PROP PISTON BEING FORMED WITH A CENTRAL BORE EXTENDING COAXIALLY WITH SAID PISTON THROUGH THE WHOLE LENGTH THEREOF; AND MEANS FOR FEEDING PRESSURE FLUID INTO AND OUT OF SAID PRESSURE CHAMBER. 